Communication between remote facilities has grown rapidly through the years and communication techniques have become increasingly more sophisticated. At the present time, it is rather commonplace to communicate with a remote facility through the use of terminals having video display screens. Data is transmitted in a manner substantially identical to that employed in television communications wherein a composite signal is transmitted and is comprised of image information representing each point in the raster, said image information being transmitted in the serial fashion. The composite signal further includes frame and line sync pulses to respectively identify the beginning of each frame of the raster and to identify the beginning of each line of a raster. This technique allows a screen display to be developed quite rapidly. Obviously, the display is continually refreshed, as is also conventional.
Although it is quite convenient to provide a display screen for communication of image information, it is also advantageous to be able to generate a printed copy of the information displayed on the screen for a variety of purposes, such as record keeping, subsequent evaluation, and the like. Techniques have been developed to print data appearing on the screen of the video display device and are presently in use. For example, some of the techniques presently available are disclosed in the following United States Pat. Nos.:
3,685,039 issued Aug. 15, 1972 PA0 3,618,032 issued Nov. 2, 1971 PA0 4,021,608 issued May 3, 1977 PA0 4,165,520 issued Aug. 21, 1979 PA0 4,148,066 issued Apr. 3, 1979 PA0 4,084,195 issued Apr. 11, 1978
The apparatus employed in the above-mentioned patents is quite complex and expensive. For example, U.S. Pat. No. 4,084,195 requires a very large memory capable of storing information representing all of the dot positions of a complete video raster. Another technique, taught by U.S. Pat. No. 4,165,520, although reducing the storage capability to eight complete lines of dot information, nevertheless requires a rather large size storage capability which, in addition, must be capable of re-circulating the eight lines of data at high speed. Although the technique of the first-mentioned patent is capable of rapidly accumulating image data, the system is large, quite complex and expensive. The technique described in the latter-mentioned patent, although less complex than that described in the first-mentioned patent, is still, nevertheless, complex and requires the use of a tedious technique for accumulating the bits of video information for printing.